Ostracode Biostratigraphy and Paleoecology of the Pliocene of the Isthmian Salt Basin, Veracruz, Mexico

Abstract

A detailed systematic and cluster analysis study of samples from the Pliocene of the Isthmian Salt Basin, Veracruz, Mexico, shows characteristic ostracode assemblages for the Encanto, Lower and Upper Concepcion, and Agueguexquite strata, and a shallowing-upward trend during the Pliocene.

The Encanto strata, the oldest unit (NI9 or upper NI8), are characterized by Ambocythere spp., Argilloecia posterotruncata, Bradleya norrnani, Krithe trinidadensis and Parakrithe spp., indicating a middle to upper bathyal environment. The Lower and Upper Concepcion beds (N19- 20) can be recognized by the presence of Actinocythereis vineyardensis. Touroconcha lapidiscola, and the abundance of Hulingsina sp. 1, Henryhowella ex. gr. asperrima, and Puriana spp. Encanto species persisting in the Lower Concepcion beds indicate an upper bathyal to outer neritic environment. The Upper Concepcion beds lack these species but instead possess abundant Cyprideis and Perissocytheridea spp., Basslerites? sp., Malzella conradi and Echinocythereis margaritifera. The Upper Concepcion assemblage indicates an outer to middle shelf environment. The Filisola and Paraje Solo samples were barren of ostracodes. Their foraminiferal and mollusk fauna indicates nearshore and brackish environments.

The Paraje Solo may be in part contemporaneous to the Agueguexquite. The Agueguexquite strata contain the youngest (middle N20), most abundant, and diverse fauna, indicating an inner neritic environment of deposition and representing a local marine transgression of short duration in the northern part of the basin. By upper Agueguexquite time brackish and continental conditions returned.